[Pw_forum] magnetic anisotropy calculation using fully-relativistic PPs

[peter]

Hi Cyrille,

At first all my calculations are not going to converge where I am using 
cutoffs of (40,400), (50,500) etc. Later I tried to find the optimal 
cutoffs following the recipe by Stefano:
http://qe-forge.org/pipermail/pw_forum/2013-February/101122.html
The optimal cutoffs are actually much lower than I was using, it's about 
(60,280).
I did several calculations using different cutoffs for finding optimal 
cutoffs, and I found the following
1) Forces on atoms are basically dependent on ecutrho, while
2) Total energies are basically dependent on ecutwfc
3) As the cutoffs increases, the SCF convergence becomes harder and harder.

best,
Yun-Peng


On 09/12/2015 03:30 PM, BARRETEAU Cyrille wrote:
> Dear Yun-Peng,
>
> >From experience I can just say that calculation using 
> fully-relativistic PP can be really difficult to converge and 
> sometimes almost impossible to achieve the desired accuracy 
> (especially since magneto-crystalline anisotropy requires very strict 
> convergence thresholds). You can play with broadening and k points 
> sampling.
>
> Cyrille
>
>
> ========================
> *Cyrille Barreteau*
> CEA Saclay, IRAMIS, SPECBat. 771
> 91191 Gif sur Yvette Cedex, FRANCE
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> DTU Nanotech
> Ørsteds Plads, building 345E
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> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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> email: cyrille.barreteau at cea.fr /cyrbar at nanotech.dtu.dk
> Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/
> ========================
> ------------------------------------------------------------------------
> *De :* pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la 
> part de yuewen.fang [yuewen.fang at gmail.com]
> *Envoyé :* samedi 12 septembre 2015 20:42
> *À :* pw_forum
> *Objet :* Re: [Pw_forum] magnetic anisotropy calculation using 
> fully-relativistic PPs
>
> Hi, Yun-Peng,
>
> Thanks for your feedback. It depends on the matter which you are 
> interested in.  I think this paper (Phys. Rev. B 86, 085135 (2012)) 
> can help you.
>
> Bests
> Fang
>
> ------------------------------------------------------------------------
>
> Yue-Wen FANG, PhD candidate
>
> East China Normal University <http://english.ecnu.edu.cn/>
>
>
> < peter <mailto:petercybertron at gmail.com>> 2015-09-13 02:16:28 wrote:
>
>     Thank you for your suggestions!
>     I tried using a small mixing beta (0.1~0.2), and tried using
>     reasonable cutoff energies (ecutwfc=50, ecutrho=500), now the
>     convergence is much better than before (converged down to 10^-6 Ry).
>     Another question is, I can find ultra-soft and PAW
>     pseudopotentials, which one is better for spin-orbit calculations?
>     I am using PBE XC functional.
>
>     best,
>     Yun-Peng
>
>     On 09/11/2015 08:08 PM, yuewen.fang wrote:
>>     Dear Yun-Peng,
>>
>>     Plz try to decrease mixing and perform some convergence tests for
>>     your cutoff energy to remove the oscillation of the energy! In
>>     addition, this oscillation could also be caused by the
>>     unreasonable smearing methods for metals.
>>
>>     Bests
>>     Fang
>>
>>     ------------------------------------------------------------------------
>>     Sent from YoMail <http://www.yomail.com/?utm_source=signature>
>>
>>     < Peter Cybertron <mailto:petercybertron at gmail.com>> 2015-09-12
>>     03:10:31 wrote:
>>
>>         Hi,
>>
>>
>>         I am working in University of Florida as a postdoc.
>>         I am exploring the spin-orbital calculations using pwscf, and I
>>         encounter a very slow convergence like this:
>>         > grep estimated scf.out
>>         estimated scf accuracy < 0.00000004 Ry
>>         ... (100 similar lines)
>>         estimated scf accuracy < 0.00000003 Ry
>>         > grep "total energy" scf.out
>>         ...
>>         total energy = -3667.91077719 Ry
>>         total energy = -3667.91078176 Ry
>>         total energy = -3667.91077642 Ry
>>         total energy = -3667.91078300 Ry
>>
>>
>>         Although the convergence of total energy seems OK (down to
>>         0.00001 Ry ~
>>         0.0001 eV = 0.1 meV), I still feel uncomfortable since I
>>         never encounter
>>         such a problem without spin-orbit interactions.
>>
>>
>>         I downloaded the ultrasoft and PAW pseudopotentials from
>>         PSLib and I am
>>         using the PBE flavor of XC functional. The system I am
>>         studying is a two
>>         dimensional magnetic insulator.
>>
>>
>>         The parameters I am using are:
>>         constrained_magnetization = 'total direction'
>>         fixed_magnetization(3) = 0.0
>>         lambda = 0.2
>>         ecutwfc = 30.0 ,
>>         ecutrho = 300.0 ,
>>         occupations = 'smearing' ,
>>         degauss = 0.005,
>>         smearing = 'mv' ,
>>         nosym=.true.
>>         mixing_mode = 'local-TF' ,
>>         mixing_beta = 0.9 ,
>>         diagonalization = 'david' ,
>>
>>
>>         Which parameter on earth keep my calculations non-converged?
>>
>>
>>         Best,
>>         Yun-Peng
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>>
>>
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